1. Field of the Invention
This invention concerns odometers in general. More specifically, it provides for a highly accurate odometer system, such that cumulative errors may be eliminated.
2. Description of the Prior Art
Heretofore, it had been difficult to manufacture an odometer system which is sufficiently accurate to avoid accumulating substantial errors where extremely lengthy linear measurements are involved. For example, in certain oil-well-drilling procedures in which linear distance is to be measured along the drill string, the measurement should be extremely accurate. This is especially so when any error is considered relative to the total depth of modern deep wells. The conventional linear measurement in such case is made from revolutions of the derrick sheave, and the sheave or other odometer wheel employed, invariably has manufacturing tolerances which result in a discrepancy when taken with practically any unit of linear measurement. Such discrepancy may be either positive or negative. But in either case, taken over the great distances involved in deep-well operations, it will accumulate a substantial and undesirable error.
Thus, it is an object of this invention to provide means for periodically making a unit correction, in order to counteract the above-indicated manufacturing error.